Objective: To determine whether in the milieu of a rapidly responding emergency medical system, a program in which dispatchers instruct callers (reporting an out-of-hospital sudden cardiac arrest) to perform chest compression will yield survival outcomes similar to those obtained when bystanders initiate CPR. It will also determine whether chest compression instructions alone will achieve better outcomes than traditional instructions involving airway management ventilations and compressions. King Counts DMS developed a traditional ABC-CPR dispatcher message. Data obtained following instrumentation of this program suggests positive results for the relatively small number of cases where the message was successfully delivered. Rationale: Several studies have found an association between bystander initiated CPR and improved survival. The improved survival appears independent of the type or degree of training of the bystander. Dutch investigators found that the arterial vessels in dogs remain fully oxygenated for at least five minutes after arrest and that external chest compression can be continued for up to at least 45 seconds before arterial PO2 drops without ventilation. Design: 1. A chest compression message for dispatcher use would be developed and tested over a period of several months. 2. A random half of the Seattle dispatchers would be taught the chest compression message and will utilize it for incoming calls involving cardiac arrest. The other dispatchers will continue to handle calls as in the past. This phase will continue for a maximum of 1 year and 9 months. 3a. If the chest compression message is found to be effective, dispatchers will alternate between providing chest compression message or the county ABC-CPR message. 3b. If the chest compression message is not found to be effective, a comparison of the ABC-CPR message and standard care will be undertaken.